Extrusion apparatus



April 9, 1963 c. J. HEFFELFINGER 3,084,385

ExTRusIoN APPARATUS 2 Sheets-Sheet 1 Filed July 8, 1959 mi IIIIIIINVENTOR CARL JHN HEFFELFNGER LQ n ATTORNEY April 9, 1963 c..1.HEFFELF1NGl-:R 3,084,385

ExTRUsIoN APPARATUS Filed July 8, 1959 2 Sheets-Sheet 2 ETW 33 www@ 39Fig. 5

HWENTOR CARI. JOHN HEFFELF/NGER BY @4A/M 972@ ATTORNEY United StatesPatent Oiiice 3,084,385 Patented Apr. 9, 1963 3,034,385 EXTRUSEQNAPPARATUS Sarl .lohn Heeiiinger, Circlevillc, hie, assigner to E. I.Pont de l Temours and Company, Wilmington, Del., a corporation ofieiaware Filed .idly 8, 1959, Ser. No. 325,321 4 Caims. (Cl. it-lil Thisinvention relates to apparatus for the continuous extrusion of films.More particularly, it relates to an improved die design for an extrusionapparatus.

In the preparation of self-supporting iilms from polymeric thermoplasticmaterials, it is usual to extrude the polymeric material in molten formthrough an extrusion die and to cast the extruded polymer as a lilm ontoa quenching device. For example, m-olten polyethylene terephthalate iscast as a iilm through an extrusion die (hopper) consisting of la slotwith parallel faces that are adjustable over their length.

One clitculty which arises in polyethylene terephthalate extrusion andwhich would also ari-se in the extrusion of most molten polymers throughan extrusion die is that degraded polymer tends .to build up on the lips-of the die. This is caused by low molecular weight materials wettingthe emergent lip and baking on the surface at the temperatures used. Thepresence of degraded polymer on the die lips produces ilow deformitiesduring extrusion. The flow deformities manifest themselves as streaks orsmears in the cast iilrn. This condition is corrected only by stoppingoperation and manually cleaning the die lips. A substantial loss ofmaterial and time is reflected in the high cost of producing such ilms.

It is an object of this invention to pnovide an irnproved apparatus forthe extrusion of thin films. Another object is to provide an apparatuswhich produces thin films of substantially uniform thickness overextended periods of operation. Other objects will appear hereinafter.

The objects 'are accomplished by a novel design for the co-acting lipmembers which deiine the slot or orice of the extrusion die, throughwhich orifice the molten polymer is extruded.

The invention will be described as it applies to hat film in the form:of sheets and the like. However, it should be understood that theinvention is applicable to the extrusion of lilm in tubular form, asnarrow ribbons or in any other form wherein .the buildup lof degradedpolymer on 'the oriice-delining lip members poses a problem.

in an extrusion apparatus of the slotted die type suitable for theextrusion of molten polymeric material in the form of la film whereinthe exit path of the extrudate is deiined by the orifice-definingessential edges of a pair of lip members, the impnovement in design thatis the subject lof the present invention comprises a pair of partiallyparallel, partially -diverging essential edges of lip members of depth1), the mutual divergence of said essential edges being vfor a distanceequal to about 0.5- 0% -of the depth 3), the divergence terminating atthe plane containing the lines defining `the outermost edges of said lipmember-s and the divergence of each essential edge being such that astraight line drawn from the 'outermost `edge of the lip member to thepoint at which divergence starts makes Ian angle of -60 degrees with theplane defined by the extension `of the parallel portions of saidessential edges of the lip member-s.

The divergence may take the preferred form of a straight line in eachlip member, ie., chamfered or beveled edges, or each edge may be roundedto present a pair of convex surfaces. If each edge is rounded, itispreferred that the roundness be formed according 'to a regular geometricpattern so that the rounded surface represents a section of anellipsoid, hyperboloid, paraboloid or cylinder.

The invention will be more clearly understood by referring to thedrawings which follow, in which:

FIGURE 1 is a side elevation with parts in section of the extrusionapparatus;

FIGURE 2 is a chess-sectional view taken substantially along the line2--2 of FIGURE 1',

FIGURE 3 is ran enlarged sectional View of the essential edges of hopperlips within the scope of the present invention;

FIGURE 4 is an enlarged sectional view of another modilication withinthe scope of the present invention of the essential edges lof the hopperlips; land FIGURE 5 yis an enlarged sectional view of the essentialedges of hopper lips of the prior art.

Referring now to FlGURES l and 2, the film extrusion apparatus comprisesa main body member 1 composed of 1a metal having a flat bottom Z. Anenlarged U-shaped longitudinal channel 3 is located in the center [ofthe body, the spaced side walls of the channel terminating in twolongitudinal edges where they meet 'the bottom. Fitted in channel 3 is a`similarly shaped longitudinal sleeve 4. The side wells of this sleeveare welded to the body member at the longitudinal edges where thechannel meets the bottom wall. The lengthwise opening. 5 between thesleeve edges constitutes .a wide orice or |outlet from the sleeve. Theouter Wall of the sleeve is spaced from the channel walls .so .as toprovide a space for the circulation of a heat-exchange lluid. Aplurality of diagonal passages 6 communicate with said -space and withhorizontal `passagers 7 in end plates 8 which are Iheld to body member 1by means of bolts 9. Aixed to each end plate 'by a weld joint is abell-shaped hub 10 which is adapted to receive la metal tube 11 having`a flared or frustroconical portion i12. the inner end of which abutsthe end fof sleeve .4. The hub has `a smooth cylindrical portion 13which is journalled in a suitable bearing on a frame (not shown). Theend yof the hub is shaped to receive a cap 14 which has a hole 15interlitting with the outer surface of the tube. This cap can be fixedto the hub by means of screw threads, a weld, or other suitable means,or it can be force-fitted onto the hub. A worm gear 16 is placed overone cap and attached to it by a suitable means, for example by means ofscrew V17' threadably engaged with lug 18 on the collar. The outer wallsof tube l1 are `spaced from the inner Walls of the bellshaped hub forthe circulation of la heat-exchange fluid. A plurality of openings 19are provided in the ends of the cap and they communicate with a suitablesource of heat-exchange Huid.

The' other hub has a collar 2@ with a lug 20 which can be fastened yto'a frame member after the hubs and assoeiated extrusion device areadjusted, by means of the worm gear and associated means (not shown), tothe desired position.

Beneath the body member and fastened thereto on each side of thelengthwise slot opening 5 in the channel sleeve, there are disposed twoco-acting lip members 21 which are U-shaped and substantially identicalin construction except that they are reversed in position. The upper arm22 of each lip member 2l has a flat upper surface which tits against thellat bottom surface 2 of the body member 1. The upper arm is providedwith a row of holes 23 preferably uniformly spaced through which extendscrews 24. The dat inner heads of the screws contact the inner surfaceof the upper arm and the heads are disposed in lateral open-ended slot25. These screws are threadably engaged with suitable threaded holes 26in the bottom surface of the body member.

In bottom arm 27 immediately beneath each screw head is a hole 2S forthe insertion of a tool to adjust the screws. A narrow lateral slot 29extends from each hole to the outer edge of the lower arm of theU-shaped member 2l.

The bottom web or inner end walls 30 ot each lip member 21 slants formost of its length and together they form a tapered orifice to leadfluid from the channel sleeve to the orice-delining lip portions oressential edges 31 of the end walls of the lip members 21.

Screws 32 which are thread'ably'engaged in respective holes 33 in theupper arm extend through similarly spaced holes 34 (of larger diameterthan the screws) in bottom arm 27. IBetween the head of each screw 32and the outer surface of the arm is a washer 35 and a coil spring` Theopen ends of slot 25 (i.e., between the upper arm 22 and bottom arm 27)have threaded arcuate portions 37 in the surfaces of such arms. Thesethreaded arcs have their bisecting Vertical plane passing through thecenter of screws. Threadably engaged with the arcuate portions aretapered screws 38 having polygonal shaped ends 39 adapted to receive atool (not shown) for adjusting them toward or away from the longitudinalaxis of the extrusion orice. Each spring insures that each segment otthe lower arm between nar-row lateral slots 29 is always in contact withthe tapered screw in the central part of such segment. The taper of thethread, the pitch of the thread and the lever ratio can be selected togive the desired mechanical advantage Ibetween screw rotation and lipmovement. While in the preferred aspect of the invention there are twoadjustable extrusion orifice-delining members, one of these can be madesolid and nonexible.

In assembling the device, the lip members 21 are fastened in the bodymember by first aligning the essential edges of the lips along an axisat approximately the spacing desired and then tightening t-he screws 24.The Width of the slot opening between the lips in each segment betweennarrow -slots 29 is measured carefully. Tapered screws 38 are thenadjusted to correct for any deviations from a straight line.

FIGURE is an enlarged sectional view of the essential orice-dening edgesof the lip members 21, as known heretofore in the prior art. It will benoted that the orice-deiining edges 311 are ilat and mutually parallelthroughout the depth D.

FIGURE 3 is an enlarged section showing the same oriiice-deiiningportion of lip members 21 as in FIGURE 5 but constructed in accordancewith the preferred mode ot the present invention. The orifice-definingessential edges 31 are mutually parallel for a distance less than thetotal depth D. At points A and A', the lip portions start to mutuallydiverge. The angle of divergence a being from 60 degrees., The distanceover which the essential orice-dening edges of the lip members divergeshould be less than one-half of the total depth D of the essentialedges, i.e., less than 50% of D. Divergence for a distance greater than50% of D provides too low a pressure drop across the lip and producesvarying llow patterns along the length of the orilice, i.e., across thewidth of the extruded film. Both of these factors yield non-uniform,unacceptable films. The minimum distance of divergence is preferably 2%oi the total depth D of the essential edges. However, divergence for adistance ment in the smoothness of the extrusion operation.

FIGURE 4 represents another embodiments wherein* the edges have beenrounded to form a section of a cyl-v inder. However, the mutuallydivergent portions starting at B and B' and the angle of divergence bshould be the same as for FIGURE 3. That is, the lip portions shoulddiverge over a distance equal to 0.5-50% of the total depth of theiressential edges" and at an angle of 10-6() degrees.

The principles and practice of the present invention will be moreclearly understood by referring to the ex amples which follow. Althoughthese examples relate tol the extrusion of polyethylene terephthalateiilm, other' kinds of materials can also be extruded in the apparatus otthe present invention with the same success obtained using polyethyleneterephthalate. Among such materials are film-forming polymers such aspolyethylene, polyvinyl chloride, copolymers of vinyl chloride and vinylacetate, polyvinyl fluoride, polymethyl methacrylate, polystyrene,regenerated cellulose, cellulose acetate, cellulose propionate,cellulose acetate butyrate, ethyl cellulose, rubber hydrochloride, etc.

EXAMPLE 1-3 In Examples h3, polyethylene terephthalate polymer preparedas described in USL Patent No. 2,465,319 to Whin-eld and Dickson wascontinuously extruded at a rate of about 1,000 pounds/hour at atemperature of 280 C. through an extrusion die of conventional design toform iilm having a thickness of 5-20 mils. The geometry of theorifice-defining essential edges of the die lips was modified inExamples 1 3, in accordance with the present invention. The total depthof the exit orifice, i.e., D, was 0.125. In Example l, the lips mutuallydiverge to form a cylindrical (rounded) surface similar to thatillustrated in FIGURE 4 of radius 0.0078; in Example 2, to form acylindrical surace similar to that illustrated in FIGURE 4 of radius0.0156; and in Example 3, to form a planar (chamfered) surface asillustrated in FIGURE 3 of depth 0.0156" having an angle of chamfer of30 degrees. As a control, the exit path defining surface of the die lips(the effective essential edge or land) having a depth of 0.125 wasconventional, i.e., of the square geometry shown in FIGURE 5.

The smoothness or continuity of operation for each case is given inTable II. The extrusion operation was stopped in order to clean the dielips when unreasonable streaks or smears appeared in the cast lm.

EXAMPLES 4-7 In order to eiect a simultaneous comparison between the lipgeometry of the present invention and the conventional square lipgeometry under identical process conditions, a special extrusion die-was constructed wherein the orice-dening lip structure was 21" inlength, the geometry of the exit-defining lips differing over three 7"sections. One edge section had a 15 chamfer with a chamfer depth of0.0l56; the center section, a conventional (square) lip geometry; andthe other edge section, a 30 chamfer with a chamfer depth of 0.0156",the total depth of the orice-defning essential edge being 0.125.

Polyethylene terephthalate polymer was extruded continuously throughthis special extrusion die over periods of time ranging from 1.5-8.5hours, With the temperature of the molten polymer and the extrusion ratebeing varied to simulate a range of process conditions. Table ll, be-

low, lists the incidence of smears (average number of smears per hour)for polymer extruded through `each of the three sections of theextrusion die described above. Table II v Polymer Temper- Length Average Ex. Lip Geometry Extruded ature of oi Run No.

of Section (lbs/hr.) Extrusion (Hr.) Smears C.) per Hour d- 4 15ucheminer. 150 200 8.5 1.8

emmer--. 150 aso a5 4.3 15 square 150 290 S. 5 14.-. 5 5 15 eharnfen-.150 280 2.5 0 30 chantier... 150 280 2. 5 0 square 150 280 2. 5 14 6 15chamfe 100 280 1.5 0.5 30 charmer. 100 280 1.5 0.5 square- 100 280 1. 512 20 7 15 chamier-.. 100 290 0.0 0

30 chamfer". 100 200 6. 0 0. 25 square 100 290 G. 0 2

EXAMPLE 8 Polyethylene terephthalate polymer was prepared as inExample 1. The polymer was extruded at a temperature of 280 C. through aconventional extrusion die with the modification that the essentialedges at the exit of the die lips were chamfered at a 30 angle with achamfered depth of 0.0156", the total depth of the orificedeiiningessential edges being 0.125. The lip opening was 0.035". Test runs `of24 hours duration Were made. Results of the performance of thisextrusion die are listed in Table lll compared to control runs in whichan extrusion die with oriee-deiining lips of regular square geometry wasused.

Table Ill Thiek- Number Average Die Lip Rate o ness of Lip Streak TestRun Geometry Polymer (gauge) Clean- Grade 1 Employed Extrudoi Cast ingsper per ed/hour Film 24 hrs. 24 hours (mils) W4 Controls:

A Square 900 5l0 4 2. 1

do 1,000 10 S 3. 5

lStreak grade-The incidence ol streaks occurring in the east film wasnoted and the film graded from 0-5 according to the severity oi streakincidence; a streak grade of 0 indicating no streak formation.

EXAMPLE 9 Polyethylene terephthalate polymer prepared as described inExample 1 was continuously extruded through a conventional extrusion diein which the exit defining lips (the essential edges of the lip members)of the die had a cylindrical coniiguration with a radius of 0.0156". Theextrusion die lip opening was 0.013". The depth of the essential edgewas 0.1094". As a control, the polyethylene terephthalate polymer Wasmelt extruded through an extrusion die having the conventional squareexit lip geometry.

The comparison of the results obtained in several tests using these twogeometric configurations is summarized in Table 1V.

Tab ze 1V Mfr/ff# Smear Rate of Tempera- Frequency Die Lip GeometryEmployed Polymer ture of (average E xtrnded Extrusion number (lhs/hr.)C.) o smears per hour) Square 150 290 135 Rounded. 150 290 1 Square 150285 140 Rounde 150 285 4. 3 Square 150 280 170 Rounded 150 280 19 Square150 290 355 Rounded- 150 290 13 Square- 150 290 94. 5 Rounded. 150 2905. 8 Square- 290 137 Rounde 100 290 6. 8

Having fully disclosed the invention, what is claimed is:

1. ln an extrusion apparatus for the extrusion of molten polymericmaterial in the form of a film wherein the exit path of the extrudate isdefined by the orificedefining essential edges of a pair of lip members,the improvement which comprises a pair of lip members, the essentialedges of sai-d lip members being partially parallel and partiallydiverging, the divergence of Said essential edges being for a distanceequal to about (L5-50% of the total depth of said essential edges, theparallel portions of said essential edges being from about 50-99.5% ofthe total depth of said essential edges, said divergence terminaitng vatthe plane containing the lines defining the outermost edges of said lipmembers, the divergence of each essential edge being such that astraight line drawn from the outermost edge of the lip member to thepoint at which divergence starts makes an angle of 10-60 degrecs withthe plane dened by the extension of the parallel portions of saidessential edges of the lip members.

2. An extrusion apparatus as in claim l wherein the divergence of theessential edges of the lip members is in the form of chamfered edges.

3. An extrusion apparatus as in claim 1 wherein the divergence of theessential edges of the lip members is in the form of cylindricallyrounded edges.

4. ln an extrusion apparatus for the extrusion of molten polymericmaterial in the form of a iilm wherein the exit path of the extrudate isdefined by the orifice-defining essential edges o `a pair of lipmembers, the improvement which comprises a pair of lip members, theessential edges of said lip members being partially parallel andpartially diverging, the divergence ot said essential edges being for adistance equal to about 2-50% of the total `depth of said essentialedges, the parallel portions of said essential edges being from about50-98% of the total depth of said essential edges, said divergenceterminating at the plane containing the lines defining the outermostedges of said lip members, the divergence of each essential edge beingsuch that a straight line drawn from the outermost edge of the lipmember to the point at Which divergence starts makes an angle of 10-60degrees with the plane defined by the extension of the parallel portionsof said essential edges ot the lip members.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN AN EXTRUSION APPARATUS FOR THE EXTRUSION OF MOLTEN POLYMERICMATERIAL IN THE FORM OF A FILM WHEREIN THE EXIT PATH OF THE EXTRUDATE ISDEFINED BY THE ORIFICEDEFINING ESSENTIAL EDGES OF A PAIR OF LIP MEMBERS,THE IMPROVEMENT WHICH COMPRISES A PAIR OF LIP MEMBERS, THE ESSENTIALEDGES OF SAID LIP MEMBERS BEING PARTIALLY PARALLEL AND PARTIALLYDIVERGING, THE DIVERGENCE OF SAID ESSENTIAL EDGES BEING FOR A DISTANCEEQUAL TO ABOUT 0.5-50% OF THE TOTAL DEPTH OF SAID ESSENTIAL EDGES, THEPARALLEL PORTIONS OF SAID ESSENTIAL EDGES BEING FROM ABOUT 50-99.5% OFTHE TOTAL DEPTH OF SAID ESSENTIAL EDGES, SAID DIVERGENCE TERMINATING ATTHE PLANE CONTAINING THE LINES DEFINING THE OUTERMOST EDGES OF SAID LIPMEMBERS, THE DIVERGENCE OF EACH ESSENTIAL EDGE BEING SUCH THAT ASTRAIGHT LINE DRAWN FROM THE OUTERMOST EDGE OF THE LIP MEMBER TO THEPOINT AT WHICH DIVERGENCE STARTS MAKES AN ANGLE OF 10-60 DEGREES WITHTHE PLANE DEFINED BY THE EXTENSION OF THE PARALLEL PORTIONS OF SAIDESSENTIAL EDGES OF THE LIP MEMBERS.